Hypersonic missiles operate in an extremely severe thermal environment, with skin temperatures reaching 6000.degree. F. There are no practical insulative materials, much less structural materials, that can survive these temperatures, particularly when combined with aerodynamic erosion. Structure must be protected either with ablative insulation or be cooled.
Certain missile guidance systems utilizing radar or optical sensors require a viewing port or window of some optically or radar transparent material. Ablation products from ablative insulators tend to obscure the sensor's view, and so, such insulators cannot be used ahead of or in the vicinity of such windows. Structure ahead of the window must therefore be cooled. The standard cooling method is to inject a gas under pressure into the flow ahead of the window (film cooling) or to pump it through holes distributed over the skin (transpiration cooling). Both systems require a very large rate of gas flow, a considerable quantity of gas under high pressure, a manifold, and a cooling control system. There are large cost, weight, reliability, and volume penalties associated with these systems.